Multicomponent Gelation through Cooperative Acid-Amine Pairing: A Combined Experimental and Computational Materials...

Cooperative gelation from nongelating molecular components offers a powerful yet underexplored route to synthesis-free soft materials. Here, we report a combined experimental and computational materials design strategy in which cooperative acid-amine pairing induces supramolecular gelation that is inaccessible to the individual components. Binary mixtures of phosphorous acid (PA) and organic amines formed gels in multiple organic solvents, despite the absence of gelation by either species alone. Among the systems studied, the PA/n-hexadecylamine (HA) pair exhibited the highest gelation efficiency. Structural and mechanical characterization using FTIR spectroscopy, X-ray diffraction, scanning electron microscopy, and oscillatory rheology revealed the formation of supramolecular networked structures. Molecular dynamics simulations provided molecular-level insight into the synergistic roles of hydrogen bonding, ionic pairing, and solvophobic interactions, with computational data showing good agreement with experimental observations. Beyond establishing a generalizable soft materials design principle based on cooperative gelation, the PA+HA gels displayed stimuli-responsive behavior, enabling expedient visual detection of metal ions and carbohydrates through gel perturbation, as well as vapor-phase sensing of amines and acids via rapid gel-sol transitions. This work demonstrates that simple, commercially available components can be programmed through cooperative interactions to yield multifunctional supramolecular gels with practical sensing capabilities, without the need to synthesize new molecules.